最近監控系統的數據庫監控總是延遲，查看日志報錯：
2015-08-27 10:20:19,534 ERROR Traceback (most recent call last):
File "oracle_mon.py", line 306, in <module>
update_status(ip, 'stop', timer.end_date)
File "oracle_mon.py", line 285, in update_status
pg.db.update("oracle_mon", where=where, status=status, stat_date=status_date)
File "/usr/lib/python2.7/site-packages/web/db.py", line 881, in update
db_cursor = self._db_cursor()
File "/usr/lib/python2.7/site-packages/web/db.py", line 566, in _db_cursor
return self.ctx.db.cursor()
File "/usr/lib/python2.7/site-packages/web/db.py", line 507, in _getctx
self._load_context(self._ctx)
File "/usr/lib/python2.7/site-packages/web/db.py", line 516, in _load_context
ctx.db = self._connect_with_pooling(self.keywords)
File "/usr/lib/python2.7/site-packages/web/db.py", line 970, in _connect_with_pooling
conn = DB._connect_with_pooling(self, keywords)
File "/usr/lib/python2.7/site-packages/web/db.py", line 563, in _connect_with_pooling
return self._pooleddb.connection()
File "/usr/lib/python2.7/site-packages/DBUtils-1.1-py2.7.egg/DBUtils/PooledDB.py", line 331, in connection
con = self.steady_connection()
File "/usr/lib/python2.7/site-packages/DBUtils-1.1-py2.7.egg/DBUtils/PooledDB.py", line 279, in steady_connection
*self._args, **self._kwargs)
File "/usr/lib/python2.7/site-packages/DBUtils-1.1-py2.7.egg/DBUtils/SteadyDB.py", line 134, in connect
failures, ping, closeable, *args, **kwargs)
File "/usr/lib/python2.7/site-packages/DBUtils-1.1-py2.7.egg/DBUtils/SteadyDB.py", line 186, in __init__
self._store(self._create())
File "/usr/lib/python2.7/site-packages/DBUtils-1.1-py2.7.egg/DBUtils/SteadyDB.py", line 190, in _create
con = self._creator(*self._args, **self._kwargs)
File "/usr/lib64/python2.7/site-packages/psycopg2/__init__.py", line 179, in connect
connection_factory=connection_factory, async=async)
OperationalError: 致命錯誤: 已保留的連接位置為執行非復制請求的超級用戶預留
查到數據庫使用的活動連接數為90左右，而pg的默認最大連接數MAX_CONNECTION=100，懷疑是數據庫連接數過多導致報錯。
事實果然如此，老數據庫的MAX_CONNECTION=200，並沒有使用默認的100。
解決辦法：修改配置文件（postgresql.conf）中的默認最大連接數MAX_CONNECTION=200，重啟數據庫即可。
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原文鏈接：https://blog.csdn.net/kmust20093211/article/details/48037819/